This invention relates to well drilling equipment including a direct drive drilling unit. More particularly, the invention relates to apparatus and a method for moving the drilling unit from a well centerline position to a position laterally offset from the centerline of the well during tripping, when performing maintenance or when lining the well with casing.
Conventional rotary drilling includes a rotary table, a motor mounted on or below the derrick floor for rotating the table, and a kelly for rotationally connecting the table to a drill string. In recent years, these drilling units are being replaced by or retrofitted with direct drive drilling units. A direct drive drilling unit is suspended from a traveling block for vertical travel within a standard derrick or mast, hereafter referred to as a derrick. The drilling unit is mounted on a carriage connected to a pair of vertical guide rails secured to the derrick.
A direct drive type drilling unit includes a motor drive assembly and a pipe handling assembly. The drive assembly includes a drill motor connected to the drill string by a cylindrical drive sleeve or sub assembly extending downwardly along the centerline of the well from the drill motor. Drilling is accomplished by the powered rotation of the drill string by the drill motor.
A cutting tool or bit is threadably connected the bottom of the drill string which, through the rotational energy supplied by the drill motor, cuts through the earth formation and deepens the well. As the well is drilled, the bit becomes worn and periodically must be replaced. When replacement of the bit becomes necessary, a portion of the drill string corresponding in length to one or more sections of drill pipe is removed from the well and pulled above the derrick floor. This portion of the drill string is removed to a pipe storage rack on the derrick. The drill string again is pulled from the well exposing the next pipe section above the floor which is similarly removed. This sequence, usually referred to as tripping out, is continued until the entire drill string is removed from the well. The bit on the bottom of the drill string is replaced and the drill string is then reassembled; i.e. tripping in, by connecting all the pipe sections previously removed.
Sometimes it is undesirable to use the drilling unit to remove or add the pipe sections to the drill string during the tripping sequence. It also may be undesirable to support a long length of casing from the drilling unit when running casing liner into a well since supporting the entire weight of the drill string or well casing using the drilling unit handling assembly may cause additional wear of the drilling unit. It may be desirable to remove the drilling unit from the traveling block and use conventional hoisting equipment for supporting the drill string or the well casing. The connection between the lower end of the drive sleeve and the upper end of the drill string is broken, the drilling unit is disconnected from the traveling block, and then the drilling unit is laterally displaced away from the centerline of the well. Conventional hoisting equipment is attached to the traveling block for directly supporting the drill string or well casing during the tripping sequence or when lining the well with casing.
It is known to provide for lateral movement of a direct drive drilling unit between a drilling position and a position offset away from the axis of the well. U.S. Pat. No. 4,458,768 discloses a direct drive type drilling unit suspended for vertical travel within a derrick. The drilling unit is mounted on a carriage connected to a pair of guide rails. The guide rails extend parallel to the well axis and include an upper portion and a lower portion. The lower portion of the rails extends downwardly to near the floor of the derrick. One of the rails of the lower portion is pivotally mounted for swinging the drilling unit from the drilling position to a position offset away from the axis of the well. U.S. Pat. No. 4,437,524 discloses a similar arrangement for lateral movement of the drilling unit. The rails again include an upper portion and a lower portion. Both of the rails of the lower portion are rigidly connected to horizontal and diagonal elements forming an integral framework with the entire framework being mounted to the derrick for swinging movment about the well axis. When moved to the offset position, the drilling unit is replaced with conventional hoisting equipment that is attached to the traveling block. The traveling block is mounted on a carriage connected to the rails. During drilling of the well, the drilling unit can travel the full length of the derrick utilizing both the upper and lower portions of the rails. During tripping with the drilling unit in the offset position; however, travel by the traveling block carriage is restricted to only the upper portion of the rails. Travel by the carriage along the lower portion of the rails is prevented because one or both of the rails of the lower portion supports the drilling unit in the offset position with travel by the carriage being blocked along that portion of the lower rails supporting the drilling unit. When one or both of the lower rails are used to support the drilling unit in the offset position, it is difficult to use conventional hoisting equipment during tripping or when lining a well. When maintenace is required on the drilling unit, it also is difficult to continue drilling using conventional rotary drilling equipment with the drilling unit in the offset position. Temporarily storing the drilling unit in an offset position so close to the derrick floor allows the mud and service lines to be suspended close to the work area. This creates an unsafe environment because it adds to the clutter on the derrick floor for the drilling operators with the mud and service lines being subject to possible damage. Locating the pivot point near one of the rails of the lower portion causes the mud and service lines to become twisted 90.degree.-180.degree. when rotating the drilling unit to the offset position causing possible damage to the lines.
Accordingly, there remains a need for an apparatus for moving a suspended direct drive type drilling unit to a position offset from the well axis so that suspended hoisting equipment can freely travel the full length of the derrick or permit conventional rotary drilling equipment temporarily be used. There also remains a need for an apparatus that allows the drilling unit to be positioned in the offset position without restricting drilling operator movement under or around the drilling unit while in the offset position or causing damage to the mud and service lines. There remains a further need for an apparatus that conveniently allows a direct drive drilling unit to be installed in or removed from the derrick.